1. Field of the Invention
The present invention is related to methods and systems for guiding and controlling marine surface ship or other autonomous platforms.
2. Background
The development of autonomous marine surface vessels (i.e., ships) necessitates the integration of the guidance system with the control algorithm. This is particularly true for under-actuated vessels in which the system has six rigid body degrees of freedom while the control actions are limited to the propeller thrust and the rudder torque. The propeller thrust is devoted for the surge speed control. The rudder torque yields the desired rudder angle of attack, which is relied on to steer the marine vessel to the desired trajectory. Coupling the controller with the guidance system enables the steering control problem to simultaneously address control issues pertaining to sway displacement and ship heading.
A guidance system should provide a desired heading angle that aims at reducing the distance between the current location of the ship and the desired trajectory. Such a distance is referred to as the cross-track error. A guidance system based on the line-of-sight (LOS) concept are known in the prior art. These initial LOS guidance systems incorporate a constant radius thereby rendering such systems inapplicable whenever the cross-track error exceeds the radius. More recent LOS guidance systems have proposed varying the radius linearly with the cross-track error. This enables such guidance systems to cope with any cross-track error.
Accordingly, there is a need for improved methods and systems of guiding and controlling a marine surface vessel trajectory.